Light Emitting Diodes (LEDs) are rapidly becoming today's leading lighting technology thanks to their ability to provide high quality light at very low power levels with the potential for extremely long life.
Existing LED lighting solutions typically utilize AC input power at each lighting fixture and direct current (DC) power to drive the LEDs. An AC to DC converter stage is contained within each fixture to provide the DC power used to drive the LEDs contained therein.
Also available are LED fixtures which lack the AC to DC converter stage, hereinafter referred to as DC-DC LEDs. These lights utilize DC input power at each lighting fixture and DC power to drive the LEDs, however, since AC is typically supplied because of inherent transmission advantages, these fixtures will still require an AC to DC conversion stage to function. The AC/DC converter stage, in these fixtures, typically resides outside the light fixture itself and produces the necessary power for several light fixtures. Such light fixtures may also require the use of more than one source of power to prevent DC power transmission related issues, such as dimness or a reduction in color accuracy at a far end of such a system.
Despite these inherent limitations, a DC-DC system architecture may allow for a reduction in the size and cost of the lighting fixtures, while increasing their efficiency, since such a design eliminates the need to convert AC power within the light. Such a design enables a systems engineer to optimize the size and weight of an external power converter, achieving efficiencies which could not be achieved when designing each fixture for general usage.
LED fixtures which use unconverted AC input power to directly drive LEDs (hereinafter AC-AC LEDs) are also available. In AC-AC LEDs, the AC waveform is typically applied directly to the LED string. Drawbacks of current AC-AC light designs over AC-DC and DC-DC LED systems are that current AC-AC lights have reduced levels of controllability, due in part to the need to accommodate constantly fluctuating current and voltage input.
Another problem with AC-AC LED control is that fluctuations in the AC line peak voltage level can result in noticeable flicker in the light output. This problem is particularly severe in aircraft systems, since power is typically derived from an engine mounted generator, the output of which is impacted by changes in engine speed as well as other loads on the aircraft's limited resources.
Although today's LEDs may be robust, associated enabling circuitry often prevents the LEDs from fully delivering on their promised benefits of low per lumen power consumption and long life, while adding weight, complexity and sources of inefficiency. To enable use of this technology in aircraft and similar industries, reliability, at least, must be improved.
An additional issue relevant to commercial aircraft is systems health monitoring. Aircraft health monitoring involves the use of airplane data to provide enhanced fault forwarding, troubleshooting, and historical fix rates to reduce schedule interruptions and increase maintenance efficiency. While today's commercial aircraft have a great deal of health monitoring capability in other areas; the cabin is a black hole in this regard. One of the greatest needs for health monitoring in the cabin is in LED lighting, since LED lights degrade over time and their color characteristics change. This is especially applicable to large arrays of LED fixtures, commonly used as intricate mood lighting in modern passenger airliners, where even small differences in lighting may be noticed by a discerning traveler. The age of lights in such an array may also significantly vary, such as when a failed fixture is replaced, exacerbating such problems.
What is needed, therefore, are techniques for improving the reliability and uniformity of full color aircraft LED solutions while reducing their weight and complexity and increasing their efficiency and controllability.